Apparatus for testing transmission lines



`ian. 2l, 1947. A

A. F.'w||l soN APPARATUS FOR TEST-ING TRANSMISSION LNES Filed May 15, 1943 INVENTOR BY E715/'Aww mnwg..

ATTORNEY `,with the transmission of., signals thereover.

Patented Jan. 21,` 1947 APPARTUSIFOR 'IEES TING iTRANSMISSION INES AustingFisherf'Wilson, Brooklyn, N. Y., assignor `Lto f American 'Telephone and' Telegraph Y(Com- -pany; a corporation oNew York l `This invention relatesto transmission systems such, for example, as telephone systems, and more particularly to arrangements for `rnakingftests on the :lines `of i such systems.

I It has been knownthat a certain lsofcalled in- ,L sulation resistance `exists between a transmission dine, suchas a telephone line or cable,n and-ground, ,and that this resistancewill.vary.A due to .Weather ,conditions or variations in the insulation ofthe -line or` other causes. 4rAvariation. in, the insulation resistance` between such a line or .cable and ground beyond 4certain vlimits is aptto .interfere Accordingly inthe maintenanceoi suchlines it, is desirable to make periodic., tests to `Ndetemiine Whether .the insulation resistance betweensuch lines and. ground has varied' beyond desirable limits. It is.a1so,desirable to make -periodic tests Ato determine Whether/the` conductorsof a line have become grounded or shortfcircuited to each other. .It isI one ofthe objectsotthis invention to `provide an, arrangement .fon rapidly. and accurately making such tests. Another,object` of theinvention is-toprovide arrangements formaleing such tests Whichwillibev suitableforuseon a plurality of diierent types of-lines, including multiparty lines, Without` `causing-.any interference V.with `signaling apparatus associated .with said-lines. Other objects andA featuresfof the invention-.Will` appear V.more iullyolnthe detailed 4description thereof hereinafter-given.

`In the pastl certain types of devices for .testing lineshave been provided Awhich 4utilized `aplu- 'ralityi of normally inert gas-lledi discharge tubes. When circuit arrangements i associated .with these tubes Were connected to the aline to. be tested, .these tubes would- -remaininert if the `condition `of-` theline 'Wasr satisfactory,- butwould `break. `down and operate an alarm, -if thecondition-oi the `line was unsatisfactory z duepiorA example, to a poori insulationV resistance,` a` groundorf a short circuit. A testing; devicelof this character may =be `found in anA application;serialNo. 36,011,

led i March 5 24,. 19.42, now.; Patent: No., 2,361,013, dated J ani 9,1945, in thename of RivMfEdmonds. `While .testing-'devices of this..r character may operatersatisfactorily on v,certain .types of lines, nevertheless when connectedtor certainqother types of lines;` they may cause'interferencewith signaling apparatusV at 1 thev2 stations Yassociated with isuch. lines. -For exampla. a` multipartytelephoneline mayl have a `plurality `of: stationsl con nected` thereto .each of-which-would fha-ve, signaling devices connected thrltlghrtheimedium l.of-r a: gasffilledf; discharge; tube fbetWeen-fonesside l .of the line, and ground. Ifa testingfdevice ofthe GT/'pe disclosed in- Athe aforementioned application .were connected toD such,` a line, i the, fully voltage of the-battery. `associated with. the, gasrlled tube in. the testingset .would be, applied to the. line and.,might.cause the gas-lledtube `associated with` the. signaling ,devices at,` the stationito Adischarge, and .operate said signaling device -falsely.

The, i arrangements i offh ,thel Einventionutilize ,two

`gas-iilled tubes v.which are causedto discharge when .the-conditioncfithe linevis faulty. :How-

ever, thelcircuit arrangements ,of thegas-iilled .tubes of` theinvention are so arranged that they can7A be Aconnected to .l manyjdiiferent types of llines, particularly; to `Lrnultiparty lines, V,irzithout causing any interference4 .with orV y false, operation y.of signaling` apparatus atL..the; stations on.` `such lines.

i The. invention may be. *more*v fully understood .from the :following description together with ,the

Aaccompanying drawingin the Figures` 1, Zand 3 of. Whichtheinvention is illustrated. .Eigs. 1 and 2; show schematicallythe principlesof, the-013.61m-

`tion of, the invention, 3 is l a, moredetailed circuit Kdiagram of l. the testing set oithaimlcntion. r, Similar .reference characters ,i have,been .utilizedto denote like aparts in alloiofthe iigures.

fAs `-xlieretoiore pointed tout, -this yinvention utilizes twoanorrnallydnert; gas-.filled l .discharge tubes. l One-oi these, may. be connectedhjofthe tip conductor and thefother to the ringfconductor of the line. A faulty` icondition,,omeithen vcontductor' will cause the. tube connected. .theretoto `break-downand-cause analarm. .,A short circuit from one conductor`V -tof another -.Wi1l causa both tubestobreakidown, A. In Figs.. 1A and lare shown `schematically how.: each tube i. ,is Y connected for testing .purposes to :each side l of .the line.

In Fig. 1 is showna;gasffllleddischarge-tube .Tr-having `electrodes VI, 2 andriS. Electrodes I and;A 2 gare-the controlfv electrodes,v and@ electrodes Control 4trode i. -'I;his arrangement mayybefconnectedito the tip; conductori2-ofl-tl51eE line to belltlested. The;lnemay be a-multipartwlnegand hai/ewa Pluralitv'l'of subscribersi sets?,-ccnnectedithereto each Of whicites isiwell known-.in theartwpuld have; Signaling rdevicesa auch f es l `I 5. connected from-ne oaanothensides of thaline togroilfzld T1 are connected to the line.

may control an alarm (not shown).

tip conductor is not grounded, the net voltage applied across the control electrodes I and 2 of tube T1 will be 90-22-:68 volts, or belowthe breakdown voltage of the tube T1. Accordingly if the insulation resistance R5 is not faulty, and

the tip conductor I2 is not grounded, the voltage normally applied to the control electrodes of tube T1 is not sufcient to break it down, and it remains inert and the alarm controlled thereby does not Operate.A However, if the tip conductor I2 is grounded, orthe insulation resistance R5 falls below a certain desired value, the following circuit will be closed: from ground II, battery I0, resistance R2 and R1, tip conductor I2, insulation resistance Rs to ground. This will cause current to flow from battery Il) through resistance R2 and R1, and will cause a voltage drop to take place in resistance R2 and the part of R1 which will nullify a portion of the opposing effect of the voltage of battery I I) with respect to battery 8. y Accordingly sufficient Voltage from the 90-volt battery 8 will now be applied across the control electrodes I and 2 of tube T1 to cause it to break down and operate an alarm. Let it be assumed for purposes of illustration that the gas-lled tube T3 also has a breakdown voltage in the neighborhood of 75 volts. When the circuit arrangements of tube T1 are connected to the tip conductorv I2, the following circuit may be traced: from ground II, control electrodes of tube T1, 90Volt battery 8, tip conductor I2, control electrodesV of tube. Ts to ground. From the foregoing it will benotedthat both tubes T1 and T3 are connected in series with the 90volt battery 8, when the circuit arrangements of tube While the voltage of the battery 8 would be suicient to break down either tube alone, itis obviously not sufficient to break down either one when they are both connected in series with the battery under the 'values assumed of battery voltage and tube breakdown voltage. Accordingly it will be seen that when the arrangements of the invention are connected to the tip` conductor of the line, the voltage applied to the line thereby, in the case of a multiparty line especially, will not cause any interference vwith or false operation of signaling apparatus on the line. v

In Fig. 2 is shown a gas-filled discharge'tube T2 having electrodes `Il, 5 and 6. 'Electrodes t and 5jare the control electrodes, and electrodes 5 and 6 are connected to a work circuit I6 which Control electrode 4 is connected to battery I1, and this is connected through a portion of resistance R3 and through resistance R4 to battery 20 which is connected to control electrode 5.V A ground 2| is connected between battery 20 and control connected to ground through the gas-filled discharge tube T4. For purposes of illustration let it be assumed that the gas-lled tube T2 also has a breakdown voltage in the neighborhood `of volts, and that the gas-filled tube T4 will have a similar breakdown voltage. Let it be assumed that batteryl'l is 90 volts and battery '20 is 22 volts. The voltages of these batteries oppose each other. Accordingly if the insulation resistance Rs is above a desired Value and the ring conductor is not grounded, the net Voltage applied across the control electrodes 4 and 5 of the tube T2 will be 90-22=68 volts or below the breakdown voltage of tube T1 and the tube T2 will not operate. However, if the ring conductor is grounded, or the insulation resistance Re falls below a certain value, the following circuit will be closed: from ground 2l, Abattery 20, resistances R4 and R3, ring conductor 23, insulation resistance Re to ground. vThis will cause current to flow from battery 20 through resistances R4 and R3 and will cause a Voltage drop to take place in resistance R4 andV part of R3 which will nullify f a portion ofthe opposing effect of the voltage of battery 20 with respect to battery l1. Accordingly sufficient voltage from the -Volt battery il will now be applied across the control electrodes 4 and y5 of the tube T2 to cause it to break down and operate an alarm. When the circuit arrangements of tube T2 are connected to the ring conductor 23 of the line, the following circuit may be traced: from ground 2|, control electrodes of'Tube T2, battery I1, rin-g conductor 23, control electrodesl of tube T4 to ground. Again it will be seen that whenthe Vtesting arrangements of the invention are connected to the ring side of the line that the tubes T2 and T4 will be connected in series with the 90-volt battery I1, and the voltage from battery Il, as inthe case of the arrangements of Fig. 1, will not cause the tube T4 to break down, and hence will cause no interference with or false operation of signaling apparatus on the line.

Under certain conditions the tip and ring conductors might be short-circuited. Let us assume, to illustrate this condition, that a connection exists between the tip conductor I 2 of Fig. 1 and the ring conductor 23 of Fig. 2. A circuit may then be traced as follows: from ground II of Fig. 1', battery I0, resistances R2 and R1, tip conductor I 2, over the short circuit between the tip and ring conductors, over ring conductor 23, resistances R3 and R4, battery 20 to ground 2l of Fig. 2. In this circuit the batteries I0 and 2E) will bein a series-aiding condition. This will cause current to flow from battery It), through resistances R2 and R1, and will cause current to now from battery 23, through resistances R3 and R4, and will cause Voltage drops to Vtake place in said resistances which will nullify the opposing effect of the voltage of battery It with respecttoV battery 8, and will also nullify the opposing effect of the battery 2D with respect to battery Il. Under these conditions the amount of voltage from the bat'- tery 8 applied to the control electrodes of tube T1 Vwill be above its breakdown value, and the tube T1 will operate, and the amount of voltage applied from battery Il across the control electrodes ofvtube T2 will be above the breakdown voltage of said tube and will cause it to operate. Accordingly when a short circuitv exists between the tip and ring conductors of the line, both tubes v'11 and T2 will operate and cause their respective alarms to function. l A

In Fig. 3 there is shown-in greater detailthe circuit arrangements ofthe testing set of this invent-ion.l As heretoforepointed out, similarref'- erence characters have been used to denote like parts with respect to Figs. 1 and 2. Two gasiilled tubes T1 and T2 are provided, the tube T1 being arranged tobe connected ove-1` conductor 28 to the tip side of a line L to be tested, and the tube T2 being arranged to be connected over the conductor 29 to the ring side of the line L to be tested. The tube T1 has its control electrodes interconnected by means of batteries 8 and I0 and resistances R1 and R2, as in Fig. l. The tube T2 has its control electrodes interconnected by means of the batteries I1 and 20 and the resistances R3 and R4, as in Fig. 2. Instead of having separate grounds, such as Ii and 2l of Figs. 1 and 2, respectivelys a common ground 30 is provided in Fig. 3. To connect the testing set to the line L to be tested a key K2 will be operated which will cause the relay to operate and connect conductors 28 and 29 to the tip and ring contacts of the jack J, respectively. A cord 2l may then be utilized to connect the tip and ring contacts of the jack J to the tip and ring contacts of the line L to be tested. When the test set is connected to the line, the tubes T1 and T2 function in the same manner as described with respect to Figs. 1 and 2. Connected to conductors 28 and 29 are the resistances R'z and Re. These may be bridged across conductors 2B and 29 by operating the key K1. With the key K1 operated and the key K2 not operated, these resistances R7 and Ra may be used to simulate a connection to an actual line for purposes of calibration.

The work circuit 1 of the tube T1 terminates in a winding of a transformer 3l. The other winding of this transformer is included in a circuit connected to an alternating source of current 33. The work circuit IB of the tube T2 includes the winding of a transformer 32, the other winding of which is included in the circuit including the source 33. Included in the work circuit 'l is a relay 34. When the tube T1 breaks down, the relay 34 will operate and open a short circuit around the lamp causing it to operate and give an alarm. Due to the fact that the source 33 is an alternating current source, the relay 34 will operate intermittently and thus cause the lamp 35 to give a hashing signal. In a similar manner there is provided in the work circuit IB a relay 36 which, when the tube T breaks down, will operate and open a short circuit about the lamp 31 causing it to operate. The relay 3B will also operate intermittently and thus cause the lamp 3T to flash.

While the invention has been disclosed as embodied in certain specic forms which are deemed desirable, it is understood that it is capable of embodiment in many and other widely Varied forms without departing from the spirit of the invention as dei-ined by the appended claims.

What is claimed is:

1. Apparatus for testing a transmission line comprising a normally inert gas-lled discharge tube, a circuit interconnecting the two control electrodes of said tube, two sources of potential in said circuit, said sources of potential opposing each other, a resistance in said circuit between said sources of potential, and means for connecting said resistance directly to the line to be tested, the constants of said sources of potential and said resistance being such that the voltage drop across said resistance due to the insulation resistance of the line will cause the net voltage of both of said sources applied across the control electrodes of said tube when the insulation re-A 6 sistance vof the line'isabove a desired value to be insdicient to cause `said tube to break down, but when the insulation resistance of the line falls below said desired val-ue to be sutcient to cause said tube tobreak down.

2. Apparatus for testing a multiparty transmission line which would have lat each station connected thereto a signaling device operated by the breakdown of a gas-filled discharge tube connected between one side of the line and ground, said apparatus comprising a normally inert gas-lled discharge tube, a circuit interconnecting the control electrodes of said tube, a source of potential in said circuit, the amount of potential applied to said control electrodes from said source being determined by the insulation resistance of the line to be tested, and a ground so connected to said circuit that when said apparatus is connected to a line to be tested the gaslled discharge tube connected at a station from one side of said line to ground will be connected in series with said normally inert gas-filled tube in said apparatus and the potential from said source will be insufcient to operate the gas-filled tube connected at a station from one side of the line to ground.

3. Apparatus for testing a transmission line comprising two normally inert gas-lled discharge tubes, each of said tubes having a circuit interconnecting its control electrodes, a set of opposing batteries in each of said circuits of such values that when the apparatus is not connected to a line to be tested the net voltage applied from each of said sets of batteries to the control electrodes of its respective tube will be below the breakdown voltage of the tube, means for connecting each of said circuits to different conductors of a line to be tested, and means in each of said circuits effective when the insulation resistance of the conductor connected to the circuit is unsatisfactory for increasing the net voltage applied from the set of batteries in the circuit to the control electrodes of the tube associated with the circuit to at least the breakdown voltage of the tube.

4. Apparatus for testing a multiparty transmission line which would have at each station connected thereto a signaling device operated by the breakdown of a gas-lled discharge tube between one of the conductors of the line and ground, said apparatus comprising two normally 4 inert gas-filled discharge tubes, each of said tubes having a circuit interconnecting its con-trol electrodes, a set of batteries in each of said circuits of such values that when the apparatusis not connected to a line to be tested the net voltage applied from each of said sets of batteries to the control electrodes of its respective tube will be below the breakdown Voltage of the tube, means for connecting each of said circuits to different conductors of a line to be tested, and means in each of said circuits effective when the insulation resistance of the conductor connected to the circuit is unsatisfactory for increasing the net voltage applied from the set of batteries in the circuit to the control electrodes of the tube associated with the circuit to at least the breakdown Voltage of the tube, each of said circuits being so arranged that when either circuit is connected to a conductor of a line to be tested, the gaslled discharge tube connected to said conductor at the station will be connected in series with the gas-lled discharge tube associated with the circuit connected to the conductor.

5. .Apparatus for testing a transmission line 7 comprising a gas-lled discharge tube, a circuit interconnecting the control electrodes of said tube, said circuit including in the following sequence a battery connected to one control electrode, a first resistance, a second resistance, a second battery connected to the other control electrode of a smaller but opposing voltage to said rst battery and a ground between said second battery and the control velectrodeA connected thereto, the net voltage applied from said batteries being normally below the breakdown voltage of the tube, and means to connect a portion of saidV rst resistance to a conductor of a line to be tested.

AUSTIN F. WILSON. 

